Abstract: Influence of weld thermal cycle and restraint strain on microstructure and mechanical properties of welding coarse grained region of EH36MOD controlled rolling steel is investigated. The experimental results show that there are different microstructure in welding coarse grained region under two different thermal cycle conditions. During t8/5=6s, the microstructure is low bainite and lath martensite primarily. And during t8/5=50s, pre-eutectoid ferrite and upper bainite is main. The restraint strain fines not only austenitic grain, but changes structural morphology and their relative amount in coarse grained region. The tensile strength, ductile and impact toughness of coarse grained region are increased correspondingly during t8/5=6s, but the tensile strength is decreased and ductile as well as impact toughness are improved during t8/s=50s.

Key words: Mechanical property, Microstructure, Restraint strain, Weld thermal cycle